Reproductive biology of Crataeva religiosa Forst.

Transcription

RESEARCH COMMUNICATIONS
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ACKNOWLEDGEMENTS. We thank the Indian Council of Agricultural Research for financial support. We acknowledge IIVR for providing necessary facilities.
Received 16 August 2005; revised accepted 19 December 2005
Reproductive biology of Crataeva
religiosa Forst.
Shashi Bala Sharma, Anita Rana and
S. V. S. Chauhan*
Department of Botany, School of Life Sciences, Dr B. R. Ambedkar
University, Agra 282 002, India
Crataeva religiosa flowers profusely during March to
May, when it sheds all its leaves. The flowers are large,
hermaphrodite, actinomorphic and complete. Flowers
open in the evening between 1900 and 2030 h followed
by anther dehiscence at 1930–2100 h. Flowers offer
pollen and nectar to the visitors, which include honey
bees, moths, butterflies, bugs and birds. The plant is
self-incompatible and obligate out-crosser. Fruit-set is
restricted to only 22%. The beauty of the flowers as
well as fruit production are adversely affected by the
formation of floral galls induced by the insect, Neolasioptera crataevae Mani, order Diptera.
Keywords: Crataeva religiosa, floral galls, Neolasioptera crataevae, reproductive biology.
CRATAEVA RELIGIOSA Forst. (family Capparidaceae) is a
large tree distributed in the tropical zone and is common
throughout India, Myanmar and Sri Lanka, either wild or
cultivated1. It is cultivated in the gardens for its ornamental
as well as medicinal value2. Despite its usefulness, less
*For correspondence. (e-mail: [email protected])
CURRENT SCIENCE, VOL. 90, NO. 5, 10 MARCH 2006
attention has been paid to its floral biology, breeding systems and pollination mechanism. These are essential for
the conservation, improvement and establishment of cultivation to increase the frequency of occurrence of this
species. Keeping these facts in view, a detailed study on
the reproductive biology of C. religiosa plants growing in
different parts of Agra city has been made.
Flowering phenology was observed at plant and inflorescence level with reference to day-to-day flowering pattern
in twenty-five marked plants. For the latter, 200 inflorescences, selected at random from different individuals
were tagged before the initiation of flowering. These individuals were followed daily and the number of open
flowers was recorded. The open inflorescences were then
removed to avoid recounting the next day. The tagged inflorescences were followed until they ceased flowering.
One hundred flowers were sampled to record the floral
morphology and pollen characters. Anthesis, anther dehiscence and stigma receptivity were studied using various
methods as described by Shivanna and Rangaswamy3. The
number of pollen grains/anther/flower was determined
from 25 flowers following Cruden4. Pollen size was
measured with an ocular micrometer under light microscope following the procedure of McKone and Webb5.
The number of pollen grains divided by the number of
ovules per flower will yield the pollen–ovule ratio4. Pollen viability was assessed by hanging drop method after
Brewbaker and Kwack6. In vivo pollen germination was
checked by aniline blue fluorescence microscopic method
as described by Shivanna and Rangaswamy3. Breeding behaviour by autogamy, geitonogamy and xenogamy was
tested using controlled pollination studies. In order to observe the rate of natural fruit-set, two hundred inflorescences on different trees were tagged and were followed
until fruit development. Foraging behaviour of insects
and birds was recorded. They were observed with binoculars and photographed. Foraging activity during night was
observed using a torchlight. Pollination efficiency of different bees was checked by observing the pollen load on
different body parts under a microscope, according to the
procedure given by Kearns and Inouye7.
C. religiosa sheds all its leaves before the initiation of
flowering (Figure 1 a). Flowering starts from 26 March
and continues till the last week of May, with maximum
bloom in April. A limited number of flowers continues to
appear even during June and July. A flush of new trifoliate
leaves appears with the cessation of flowering by the end
of May. The inflorescence is a corymbose–raceme and
consists of 25 ± 3.0 flowers (R 19–30; Table 1, Figure
1 b). Flowers are large, hermaphrodite, actinomorphic, hypogynous and complete (Table 1, Figure 1 c). The calyx is
gamosepalous with four sepals, and corolla is polypetalous with the same number of petals that are arranged alternate to sepals (Table 1). Stamens are numerous, as many
as 25 ± 1.5 (R 18–31) (Table 1). They are polyandrous,
adnate to the base of the gynophore, longer than the petals,
bicelled and introrse. Single pistil is differentiated into
stigma and ovary. Stigma is capitate, dry and non-papillate
(Table 1). The ovary is bicarpellary, syncarpous (Table 1)
and elevated on a long stalk called gynophore. The number of ovules/ovary is 90 ± 9.7 (R 76–106), lying on two
parietal placentae (Table 1).
The flowers open between 1900 and 2030 h (Table 1).
Opening of the flowers is confined to the hours of darkness. Nectary is present at the base of the gynophore. Anthers
dehisce by longitudinal slit around 1930–2100 h. Pollen
grains are spherical, tricolpate with reticulate exine and
23.5 µm in diameter. The mean number of pollen grains
per anther is 3510 and per flower is 87,750. The ratio of
pollen grains to ovule number is 975 : 1. The stigma becomes
receptive after anther dehiscence around 2200 h and remains so until the late morning (0800–0930 h) of the next
day. In vitro pollen germination studies indicate that the
pollen grains remain viable for 16 h after anther dehiscence.
At the time of anther dehiscence, 94% of the pollen grains are
viable. However, there is substantial reduction in pollen
viability after 10 h (50%) up to 16 h (3%) (Table 2). In
vivo pollen germination studies show 58% pollen germination after 10 h (Figure 1 f ) and germination percentage is
only 7% after 16 h on the stigmatic surface (Table 2).
Each flower lasts for two days. At initial bud stage petals
are green in colour, but acquire white colour at late bud
Table 1.
Floral characters of Crataeva religiosa
Floral character
Observation
Inflorescence
No. of flowers/inflorescence
Flower
No. of stamens
Calyx
Corolla
Time of flower opening
Time of anther dehiscence
Mode of anther dehiscence
Pollen grains/anther
Pollen grains/flower
Pollen size
Stigma type
Ovary type
No. of ovules/ovary
Table 2.
Corymbose-raceme
25 ± 3.0
Hermaphrodite, actinomorphic,
complete
25 ± 1.5
Gamosepalous with four sepals
Polypetalous with four petals
1900–2030 h
1930–2100 h
Longitudinal slit
3510
87,750
23.5 µm
Capitate, dry and non-papillate
Bicarpellary and syncarpous
90 ± 9.7
Pollen germination at different time intervals after anther
dehiscence
Hours after anther
dehiscence
10
12
14
16
In vitro pollen
germination (%)
In vivo pollen
germination (%)
50 ± 0.5
30 ± 1.4
12 ± 2.62
3 ± 0.92
58 ± 0.3
35 ± 1.2
18 ± 2.50
7 ± 0.76
±, Standard deviation.
717
a
b
c
d
e
f
g
h
Figure 1. Crataeva religiosa. a, Tree in flowering; b, Flowering branch; c, Normal flower; d, Partially infested
flower; e, Fully infested flower; f, In vivo pollen germination on stigmatic surface showing pollen tubes (pt); g,
Apis dorsata; h, Psittacula krameri.
stages. At the time of anthesis petals remain white, but in
the morning of the next day they gradually turn light yellow
and finally become dark yellow by the evening. The next
morning, the petals begin to wither and by the evening
petals and anthers from pollinated flowers drop-off, leaving
718
only the sepals and pistil. Change in floral colour in Helicteres isora is well known, as the colour changes from
bluish-grey to dark red8.
The beauty of flowers as well as fruit production is adversely affected by the formation of floral galls induced by
the insect, Neolasioptera crataevae Mani, order Diptera.
Galls start developing a few days after the initiation of
flowering. Their number increases with increase in floral
density and then declines with rise in temperature. Percentage of gall formation is low in young plants, but
higher in older plants. Galls usually develop from meristematic and young tissues of the thalamus and grow towards
the base of the anther filament and gynophore, which become bulbous. Infestation of the insect on a single flower
is usually not uniform as is evident by the presence of
normal, semi-infested and fully infested floral parts in the
same flower. Quite often, the whole flower gives rise to an irregular mass somewhat depressed above and funnelshaped at the base. During gall formation, floral components are highly modified. Those near the galls are severely affected, whereas the ones away from the zone of
infection tend to be normal. Sokhi and Kapil9,10 have also
reported morphological changes in the flowers of Terminalia
arjuna induced by the insect Trioza.
Fruiting starts in the second week of April and fruits
begin to mature in the last week of May. Mature fruits
start to disperse their seeds during the second week of June.
Natural fruit-set is 22%. A sample of 200 inflorescences
consisting of 5024 flowers, selected at random on different trees at flower stages was used for estimating fruit
and seed-set rate. An inflorescence consists of 25 ± 0.5
flowers; among them 18 ± 1.2 are normal and 7 ± 0.5 are
infested. Thus, among 5024 flowers, 3641 are normal and
1383 are infested. Among normal flowers, 897 flowers
with 80,730 ovules set fruits with 50,456 seeds. Seed-set
is 62%.
Among the infested flowers, 40% is partially infested
(Figure 1 d) and 60% fully infested (Figure 1 e). None of
these produces fruits. Thus, among all the flowers on a
tree, 75% is normal and 25% infested. Among the 25%,
10% is partially infested and 15% fully infested. They are
not visited by pollinators. Considering the total flower
investment as 100%, the species loses 25% to infestation
and another 53% to flower abortion, leaving just 22% for
natural fruit-set.
Flowers are cross-pollinated as confirmed by various
hand-pollination experiments. The fruit-set percentage
through xenogamy is 92 and there is no fruit-set by other
modes of pollination (Table 3).
The flowers are visited by honey bees (Apis dorsata;
Figure 1 g, A. indica and A. florae), moths (Achoria grisella), butterflies (Pieris brassicae and Danaus plexippus),
Table 3.
Treatments
Autogamy
Geitonogamy
Xenogamy
wasps (Polistes hebraeus and Vespa sp.), bugs (Bagrada
cruciferarum) and birds, including sun birds (Nectarinia
asiatica), parrot (Psittacula krameri; Figure 1 h), koel
(Eudynamys scolopacea) and pigeon (Columba livia).
They visit the flowers between 1900 and 0900 h for nectar
and/or pollen. Of the total visits, honey bees made 61%,
moths 15%, butterflies 8%, birds 7%, wasps 6% and bugs
3%. Among honey bees, A. dorsata forage during 1900–
0900 h, whereas the other two species during 0500–0900 h.
Honey bees forage for both nectar and pollen. Moths forage after anthesis. They are attracted by the white colour
and heavy fragrance of the flowers. They forage during
1900–0100 h for pollen and nectar. Butterflies, wasps and
bugs forage during 0500–0900 h for nectar only. All insects
are pollen carriers and their frequent inter-plant movement
facilitates cross-pollination. Birds forage during 0500–
0900 h for nectar and for eating floral parts and fruits.
Sun birds forage largely for nectar, whereas other birds
visit the flowers for nectar and for eating floral parts and
fruits. While collecting nectar, all these birds contact the
stamens and stigma with their bill and forehead, both ventrally and dorsally and their frequent movements among the
conspecific trees facilitate cross-pollination.
Observations of different body parts indicate that A.
dorsata specimens have a higher amount of pollen grains
on their body than other species (Table 4). It is the most
dominant in number and visits the flowers soon after anthesis
at night, showing brisk activity up to 0730 h. Later its activity
declines and disappears at around 0900 h. This suggests
that A. dorsata is capable of collecting forage during moon
night hours. This bee is intolerant to excessively high
temperatures and has thus developed adaptations to forage
during night under moonlight. Rao and Raju11 have reported A. dorsata activity during night under moonlight on
the flowers of Pterocarpus santalinus during March–May,
to avoid excessively high temperature during daytime.
The other honey bees too restrict their foraging schedules
to the early morning time. Therefore, activities of pollinators are related to the ambient temperatures. Their activities
are being limited by low temperatures in temperate climates and high temperatures in tropical climates.
Obligate outbreeding is the predominant reproductive
strategy in tropical ecosystems, either through self-incompatibility mechanisms or various forms of functional dioecy.
Table 4.
Pollen pick-up by bees on C. religiosa as revealed by observing pollen on different body parts
Pollen grains
Results of breeding systems in C. religiosa
No. of
flowers pollinated
No. of
fruits
Fruit-set
percentage
50
50
50
0
0
46
0
0
92
Visitor species
Sample size
Range
Mean
10
10
10
420–510
350–380
200–240
448 ± 345
367 ± 310
214 ± 186
Apis dorsata
A. indica
A. florea
±, Standard deviation.
719
Most of the Acacia species in the tropical ecosystems are
found to be self-incompatible and out-crossing. Acacia
sinulata exhibits self-incompatibility, as indicated by Raju
and Rao12. Hand pollination experiments show that C. religiosa is a self-incompatible, obligate out-crosser. This
breeding system is functional only when conspecifics
bloom simultaneously and occur nearby, and requires vectors
to mediate pollen among conspecific plants.
In C. religiosa, the natural fruit-set is low when compared
to the high flower production. Different factors could affect
fruit-set. First is the floral galls formation, which leads to
loss of productivity. Secondly, the intensive pollen collecting behaviour of attending bees and their tendency to
confine to the same plant that they first forage may result
in more wasteful self-pollen transfer.
C. religiosa is of ornamental as well as medicinal importance and is an obligate out-crosser. For higher fruit-set,
conspecific trees should be planted nearby and remedial
measures should be adopted to combat infection of floral
parts.
1. Parker, R. N., Forty Common Indian Trees and How to Know
Them, A.A. Vishhkar Publ., Jaipur, 1986.
2. Anon., The Wealth of India, 1959, vol. 5, pp. 318–319.
3. Shivanna, K. R. and Rangaswamy, N. S., Pollen Biology: A Laboratory Manual, Narosa Publishing House, New Delhi, 1992.
4. Cruden, R. W., Pollen–ovule ratios, a conservative indicator of
breeding systems in flowering plants. Evolution, 1977, 31, 32–46.
5. McKone, M. J. and Webb, C. J., A difference in pollen size between the male and hermaphrodite flower of two species of
Apiaceae. Aust. J. Bot., 1988, 36, 331–337.
6. Brewbaker, J. L. and Kwack, B. H., The essential role of calcium
ion in pollen germination and pollen tube growth. Am. J. Bot.,
1963, 50, 859–865.
7. Kearns, C. A. and Inouye, D. W., Techniques for Pollination Biologist, University Press of Colorado, Niwot, Colorado, USA,
1993.
8. Atluri, J. B., Rao, S. P. and Reddi, C. S., Pollination ecology of
Helicteres isora. Curr. Sci., 2000, 78, 713–718.
9. Sokhi, J. and Kapil, R. N., Morphogenetic changes induced by
Trioza in the flowers of Terminalia arjuna – I, Androecium. Phytomorphology, 1984, 34, 117–128.
10. Sokhi, J. and Kapil, R. N., Morphogenetic changes induced by
Trioza in the flowers of Terminalia arjuna – II, Gynoecium. Phytomorphology, 1985, 35, 69–82.
11. Rao, S. P. and Raju, A. J. S., Pollination ecology of the Red Sanders Pterocarpus santalinus (Fabaceae), an endemic and endangered tree species. Curr. Sci., 2002, 83, 1144–1148.
12. Raju, A. J. S. and Rao, S. P., Pollination ecology and fruiting behaviour in Acacia sinulata (Mimosaceae), a valuable non-timber
forest plant species. Curr. Sci., 2002, 82, 1466–1471.
Received 22 July 2005; revised accepted 22 November 2005
Histological observations on the
scleractinian coral Porites lutea
affected by pink-line syndrome
J. Ravindran1,* and Chandralatha Raghukumar2
1
National Institute of Oceanography, Regional Centre,
Cochin 682 018, India
2
National Institute of Oceanography, Dona Paula, Goa 403 004, India
A pink-line syndrome (PLS) was reported in the reef
building coral Porites lutea in Kavaratti island of the
Lakshadweep archipelago. The affected corals had dead
patches colonized by a cyanobacterium Phormidium
valderianum and the bordering coral tissue was pink.
We examined the histological changes associated with the
PLS-affected tissue. Results showed that the zooxanthellae were released from the gastrodermal cells into the
coelenteron. Gastrodermal cells undergo necrosis and
detachment from the basal membrane. The basic staining of the cytoplasm in the gastrodermal cells bordering the calicoblastic layer suggests accumulation of calcium
ions. The ectodermal epithelium and calicoblastic cells
showed destruction through ‘apoptosis-like’ processes.
Cell swelling and vacuolation were observed in the
gastrodermal and ectodermal cells. In this communication we discuss how the presence of the cyanobacterium
adjacent to the PLS-affected tissue could cause the observed damage, bring about imbalance and a shift in
the coral-zooxanthellae symbiosis.
Keywords: Cellular changes, pink-line
Porites lutea, symbiosis, zooxanthellae.
syndrome,
EXISTENCE of corals is threatened by environmental
changes, pollution and direct human interference in many
coral reefs around the world. Diseases bring about destruction
of corals to a greater extent than other factors. Investigations
on diseases that help identify the factors which cause and
manifest the disease will help in the management of diseases1.
We earlier reported partial mortality in the massive coral
Porites lutea affected by pink-line syndrome (PLS)2,3.
Fungi and a cyanobacterium Phormidium valderianum were
isolated from the PLS-affected specimens. The cyanobacterium was identified as the etiological agent in the PLS
through Koch’s postulate experiments3,4. This communication reports on the cellular changes associated with the
PLS-affected corals and the interaction between the host
tissue and associated organism.
Coral specimens of P. lutea affected by PLS and healthy
ones were collected from a lagoon in Kavaratti island and
were transported in sea water to the field laboratory.
These specimens were fixed and preserved following the
standardized method4. Healthy and PLS-affected specimens
preserved in 70% ethanol were cut into small pieces of
*For correspondence. (e-mail: [email protected])
720

Reproductive biology of Crataeva religiosa Forst.

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